1. Field of the Invention
This invention relates to improvements in time-resolved fluorometers, particularly those useful for determining delayed fluorescence emission in clinical and other samples. More particularly, it relates to time-resolved fluorometers having diminshed instrument-produced background fluorescence.
2. Brief Description of the Prior Art
Fluorescent compounds are frequently used as labeling compounds in a broad range of assay systems, particularly those used for determining analytes of clinical interest. It has been recognized that many types of biological specimens in which such analytes are to be detected naturally fluoresce, thereby creating a natural background fluorescence which limits the sensitivity of the assay systems used to detect such analytes.
One approach to avoiding this problem has been the use of fluorescent labels, such as lanthanide chelates, which produce a time-delayed or time-resolved fluorescence which is measurable after the decay of the natural fluorescence of the biological sample. See, for example, Syvanen, et al.,Time-resolved fluorometry: a sensitive method to quantify DNA-hybrids, Nuc. Ac. Res., 14:1017-1028(1986).
Instruments have been developed to measure the time-resolved fluorescence produced by these assay systems. For example, Soini, et al., Time-Resolved Fluorometer for Lanthanide Chelates-A New Generation of Nonisotopic Immunoassays, Clin. Chem., 29:65-68(1983) discloses a manually operated fluorometer for assays using lanthanide chelates as labels.
Another such instrument is disclosed by Wieder, U.S. Pat. No. 4,058,732. The fluorometer disclosed here, like the one described by Soini, uses a laser light source to excite a reagent in a fluorescent assay composition and reads the time-delayed fluorescent signal with a photomultiplier tube.
Notwithstanding the avoidance of autofluorescence in biological samples achieved by time-delayed or time-resolved fluorescence, recognition of the limitations of instruments in this field in their own production of background fluorescence has not been documented, addressed or overcome.